The present invention relates to electrostatographic or xerographic printing, and more specifically relates to a paper input guide for use near a transfer zone, where an image on a charge receptor is electrostatically transferred to a sheet, such as a sheet of paper.
The basic process steps of electrostatographic printing, such as xerography or ionography, are well known. Typically an electrostatic latent image is created on a charge receptor, which in a typical analog copier or xe2x80x9claser printerxe2x80x9d is known as a photoreceptor. The suitably charged areas on the surface of the photoreceptor are developed with fine toner particles, creating an image with the toner particles which is transferred to a print sheet, which is typically a sheet of paper but which could conceivably be any kind of substrate. This transfer is typically carried out by the creation of a xe2x80x9ctransfer zonexe2x80x9d of AC and DC biases where the print sheet is in contact with, or otherwise proximate to, the photoreceptor. In general, the AC bias dislodges the toner particles which were adhering electrostatically to the photoreceptor, while the DC bias, also known as a xe2x80x9cdetack voltage,xe2x80x9d causes the toner particles to be attracted in imagewise fashion to the print sheet, thus transferring the image from the photoreceptor to the print sheet. Devices to create this transfer zone, such as corotrons, are well known.
In compact designs of xerographic printers and copiers, the close proximity of various imaging stations to one another can be a source of print defects. Specifically, in one configuration where the transfer zone is near the six o""clock position of a cylindrical photoreceptor, and the development zone is near, for example, the nine o""clock position, excess marking material, such as toner or developer, is likely to drop at various times into the paper path through which unmarked paper passes to reach the transfer zone. The presence of such marking material in the path is likely to smudge or make marks on the sheets, resulting in a print defect.
U.S. Pat. No. 3,620,617 discloses a xerographic printer in which the upward-facing opening of a transfer corotron is partially covered with a Mylar(copyright) flap. The flap prevents marking material from entering and contaminating the transfer corotron.
U.S. Pat. No. 3,850,519 discloses a xerographic printer in which the upward-facing opening of a transfer corotron is partially covered by a shield, which is electrically grounded. The shield prevents ions from the transfer corotron from affecting the transfer process before a sheet enters the transfer zone.
U.S. Pat. No. 4,891,680 discloses a xerographic printer in which the opening of a transfer corotron is contiguous with a sheet guide. The sheet guide maintains a copy sheet wrinkle-free as it enters the transfer zone.
U.S. Pat. No. 6,345,168 discloses a guide member upstream of a transfer zone in a xerographic printer.
According to one aspect of the present invention, there is provided a printing apparatus comprising a charge receptor, and means defining a transfer zone associated with the charge receptor. A guide member is associated with the transfer zone, the guide member defining a plurality of ribs thereon, the ribs being suitable for supporting a print sheet moving in a process direction relative to the transfer zone.
According to another aspect of the present invention, there is provided a printing apparatus comprising a charge receptor, and means defining a transfer zone associated with the charge receptor. A guide member is disposed upstream of the transfer zone along the process direction, the guide member defining an upper surface. Biasing means bias the guide member.